Yarn production



Dec. 5, 1944. F ALKE'R 2,364,407

YARN PRODUCT IO N Filed May 22, 1941 ZSZZ a INVEINTOR Patented Dec. 5,1944 YARN PRODUCTION Isaac F. Walker, Wilmington, DeL. asslgnor to E. I.du Pont de Nemours & Company, Wilmington, Del., a corporation ofDelaware Application May 22, 1941, Serial No. 394,617

16 Claims.

This invention relates tothe manufacture of regenerated cellulosefilaments by the viscose process and, more specifically, it relates toan improved process for spinning such filaments in continuous fashionwithout the interruptions and delays occasioned by the deposition offoreign materials at the spinneret orifices. more particularly to aprocess for spinning regenerated cellulose filaments from viscose whilematerially diminishing the formation and deposi- It relates tion offoreign materials at the spinneret orifices during the spinningoperation.

In the manufacture of artificial filaments by the viscose process, it iscustomary o extrude a viscose solution through spinneret orifices intoan aqueous acid coagulating and regenerating bath contained in a leadtrough or tank, whence the formed filaments are withdrawn and ultimatelycollected in the form of a suitable package.

The formation and deposition of foreign materials on the face of thespinneret, and even within the perforations of the spinneret whichconstitute the spinning orifices, has long been a troublesome factor inthe spinning of artificial filaments by the viscose process. Thesedeposits, sometimes referred to as spinneret craters, interfere with thecontinuity of the spinning operations in numerous ways. For example,deposits within the spinneret orifices diminish the size thereof,causing small, weak filaments to form, which frequently break duringsubsequent travel through the regenerating bath or during otherafter-treatments. Sometimes also the spinneret orifices become socompletely obstructed that little or no viscose can pass through,resulting in an off-standard product. The rapidity with which thesedeposits collect and the frequency of spinneret. changes requiredthereby constitute serious obstacles in the way of uniform, economicalspinning operations, not to mention the uniformity of the product,

Heretoiore, the presence of insoluble material in the regenerating bathhas been suspected as a cause for spinneret obstruction and resort takento periodic filtration of the bath to clarify the same by removal ofinsoluble precipitated material.

Heretofore, it has also been proposed to improve the spinningperformance by adding various substances to the viscose or to theregenerating bath in an attempt to prevent adhesion of these foreignmaterials to the spinneret face or orifices. These proposals have metwith some success but they have the serious disadvantage of furthercomplicating an already complicated chemical composition, either asviscose or as regenerating bath. Furthermore, these substances are oftenprohibitively expensive to use.

.It has now been observed that mere filtration of insoluble materialsfrom the bath has little or no retarding effect on the deposition offoreign materials at the spinneret orifices. In other words, it appearsthat the difilculty arises, not so much from the deposition of materialsalready suspended in the regenerating bath, as from the deposition ofinsoluble materials, as they are formed, in the reaction zone at theface of the spinneret. Consequently, one might filter the bath to obtaina elear'colorless solution for many years and still suffer from thedeposition of foreign materials at the spinneret orifices withoutrealizing that the formation of insoluble salts in the reaction zone atthe spinneret face is the critical factor. Furthermore, it has now beendiscovered that the deposition of foreign material on the face of thesplnneret can be substantially diminished if the heavy metal ion contentof the bath is reduced and maintained sufficiently low to substantiallyeliminate the formation of an insoluble heavy metal salt in the reactionzone at the'face of the spinneret. In the conventional processes for theproduction of regenerated cellulose from viscose the presence of leadand sulfide ions in sumcient quantity to form lead sulflde on thespinneret has now been found to be the cause of particularlyobjectionable deposits of foreign material on the spinneret. It isprobable that materials already suspended in the bath will tend toadhere to the spinnerei; face more readily when conditions are such thatinsoluble salts are formed in the reaction zone adjacent the spinneretface, since they may even be occluded in the deposition of the freshlyformed insoluble material.

' That lead sulfide should be the principal offender in the viscoseprocess as described is surprising. As is well known to those skilled inthe art, the solubility product of lead sulfide is affected by thehydrogen ion concentrationin an acid system, such as a viscose processspinning bath. Likewise, the presence of other electrolytes or changesin temperature will cause it (the solubility product) to vary. It iswell known that lead sulfide will not precipitate readily in thepresence of high concentrations of hydrogen ions. Judged by solubilitycharacteristics alone, lead sulfide would not be expected to precipitateout of a viscose process spinning bath. However, and this is asignificant point which apparently has been overlooked in the prior art,at the reaction zone in the vicinity of the spinneret face, because ofthe interaction of the sodium hydroxide of the viscose and the sulfuricacid of the spinning bath, the hydrogen ion concentration will be lowenough to permit some precipitation of lead sulfide if theconcentrations of the lead and sulfide ions are sufliciently high sothat the solubility product under those conditions is exceeded whateverit may be in absolute value. Once formed, the lead sulfide is difllcultto redissolve and may be removed to considerable extent by laterfiltration.

In the commercially operated viscose rayon processes, the commonlyemployed regenerating bath comprises an aqueous solution of sulfuricacid, sodium sulfate, zinc sulfate and glucose. The zinc sulfate and/orglucose are sometimes omitted but their presence is preferred for goodspinning performance. The presence of glucose permits reduction in theamount of sodium sulfate required. The zinc sulfate, which is sometimessupplemented in its action by the addition of nickel, cobalt or ferrousiron sulfates, makes possible the production of filaments of highertenacity.

In addition to these desirable and normally controlled components of theregenerating bath, there are also present other materials which derivefrom the impurities in the raw materials used in making up the bath,from the vessels and mechanical equipment which contain or handle thebath in use, and from impurities in the viscose, which materialsaccumulate in the bath because of the customary practice of re-using thebath in an economical spinning operation. As above indicated, it has nowbeen found that the most objectionable among the normally uncontrolledcomponents of the regenerating bath are leadand sulfur-containingcompounds.

The viscose employed usually comprises principally an aqueous sodiumhydroxide dispersion of sodium cellulose xanthate but because of theunstable character of sodium cellulose xanthate, it contains varyingamounts of sodium sulfide, thiocarbonates, etc.

When the viscose is brought into contact with -the regenerating bath,there occur, of course, a number of chemical reactions which result inthe formation of hydrogen sulfide, carbon disulfide, sulfur, thio acids,etc., in addition to the regeneration of the cellulose. Moreover, whenthe bath contains lead, as discussed above, the further formation ofinsoluble lead sulfide is in dicated. Thus, it becomes evident thatthose components of the bath and viscose which, heretofore, have beenleft uncontrolled, offer ample opportunity for the formation ofinsoluble materials in the reaction zone at the face of the spinneret,which materials, formed in that zone, may deposit on the spinneret faceor in the spinneret orifices and, in some instances, colloidal or othersuspended particles in the bath may be deposited simultaneouslytherewith so that comparatively rapid obstruction of the spinningorifices results.

The equipment used for handling the bath is princ pally lead orlead-lined equipment. The amount of lead in the bath depends then on thelead content of the raw materials, the type of lead (i. e., hard lead orchemically pure lead) of the equipment, particularly when lead heatingcoils are used, the ratio of the volume of the bath to the area ofexposed lead, the type and degree of filtration of the bath and even onthe amount of yarn being spun. The sulfuric acid employed frequentlycontains lead sulfate and may, therefore, be the source of both lead andsulfate ions in the bath.

It is, therefore, the object of this invention to substantially diminishthe formation and deposition of foreign materials at the spinneret facein the spinning of regenerated cellulose by the viscose process.

Other objects of the invention will appear hereinafter.

The objects of the invention may be accomplished, in general, byreducing the heavy metal ion content, and preferably also the sulfidecontent, of the coagulating bath in a viscose rayon process, andmaintaining the heavy metal ion content, and preferably also the sulfidecontent, of said bath sufficiently low to substantially eliminate theformation of an insoluble heavy metal salt, particularly an insolublemetal sulfide, in the reaction zone at the face of the spinneret.

The accompanying illustration is a diagrammatic perspective view showingone embodiment of apparatus suitable for use in carrying out the processof the invention.

Referring to the drawing, reference numeral ll designates a bathcontainer for a coagulating and regenerating bath of a viscose rayonspinning process. The spinning bath II is connected by means of conduitl3 to a receiving tank IS. The bath in the receiving tank l5 may bereplenished with fresh bath constituents through conduit I1. If desired,the bath in receiving tank l5 may be saturated with hydrogen sulfide bymeans of perforated conduit l9. The receiving tank I5 is connected to afilter 2| by means of conduit 23. The filter 2| is connected to anaeration tank 25 by conduit 27. Air may be passed into the bath in theaeration tank 25 through perforated conduit 29. From the aeration tank25, the bath liquid can be returned to the coagulating bath tank llthrough conduit 3| and pump 33.

The following examples are given to illustrate preferred methods forpracticing the present invention, it being understood, however, that thepresent invention is not limited to the detailed methods set forththerein.

Example 1 A suitable viscose solution, containing 7% cellulose and 6%sodium hydroxide and containing a delustering agent, if desired, is spunin the customary fashion to yield a IOU-denier, 60-filament yarn using aplatinum-gold alloy spinneret having orifice diameters of 0.0035 of aninch and a coagulating and regenerating bath containing 9% sulfuricacid, 19% sodium sulfate, 0.7% zinc sulfate and 4% glucose. The bath,before recirculation to the spinning positions, is led to a receivingtank where it is customary to add the usual replenishing materials, suchas acid, glucose, or the like, part of which may be fresh materials andpart the liquors from evaporation and crystallization treatmentsemployed to remove excess soluble salts, such as sodium sulfate, inaccordance with the well-known procedure of the art. The bath is thenfiltered at a suitable rate through an anthracite filter prepared asdescribed in detail below. From the filter the bath is led to a largecapacity aeration tank, for example, a tank having a capacity of 300gallons, where it is aerated as hereinafter described using an air flowof about 1 cubic foot per minute for every 5 to 6 gallons per minutefiow of bath through the tank. the air being forced in under a pressureof about 20 its temperature to about 45 C. and then it is led to thespinning machine. As the bath passes to the first spinneret of aspinning machine having 50 spinnerets, it has a lead content of about 3parts per million and a sulfide ion content of not more than 10 partsper million. The sulfide ion content is measured by the followingiodometric method:

Ten milliliters of 0.1N iodine solution are pipetted into a300-milliliter bottle provided with a ground glass stopper. To this areadded 100 milliliters of bath and the mixture is allowed to stand forexactly 10 minutes in the stoppered bottle. The mixture is then quicklytitrated with 0.1N sodium thiosulfate solution until the color changesto a light brown. At this point 5 milliliters of starch indicator areadded and the'titration is completed. Care must be taken to avoidoverrunning the end point because the sample itself is not alwayscolorless. As a blank titration, l milliliters of distilled water andmilliliters of 36N' H2804 are added to the milliliters of 0.1N iodinesolution in a 250-milliliter flask and the whole is titrated with 0.1Nsodium thiosulfate. The consumed iodine in the test titration. correctedfor the blank titration, measures the reducing power of the bath in millliters of 0.1N iodine per 100 milliliters of bath. Calculating thereducing power as a function of sulfide ion concentration, l milliliterof 0.1N iodine solution per 100 milliliters of bath is equivalent to 16parts per million of sulfide ion divided by the density oi the bath.

Example if sulfuric acid, 21% sodium sulfate, 4% glucose and 0.7% zincsulfate at a draw-off speed of 3,000 inches per minute. The bathrecirculated to the spinning machine is reconditioned in the mannerdescribed in Example I and as it passes to the first spinneret, it has alead content of about 5 parts per million and a sulfide content of about2 parts per million. Yarn is spun for a long period of time withoutencountering spinning difficulties caused by deposition of solidmaterials at the face of the spinneret. An even denier yarn is obtainedand substantially no broken filaments were encountered.

Example I]! A semi-delustered yam (100-denier, 100-filament) is spunfrom viscose prepared from highly purified wood pulp (7% cellulose, 6%sodium hydroxide) and containing dibeta-naphthol ether oi ethyleneglycol as a delusterant (about 0.1%) using a spinning bath similar tothat of Example II except that it contains 23% sodium sulfate. Adraw-off speed of 3300 inches per minute is employed. The bath,reconditioned as in Example I, approaches the first spinneret with alead content of about 3.5 parts per mill on and a sulfide content ofabout parts per million. An even denier yarn is spun with substantiallyno broken filaments for a very considerable period of time withoutencountering spinning dimculties caused by deposition of solid materialsat the spinneret face.

Example IV A delustered yarn is spun as described in Example III using adraw-off speed of 4000 inches per minute. The recirculated bath,reconditioned as described in Example Lapproaches the first spinneretwith a lead content of about 3 parts per million and a sulfide contentof about 12 parts per million. Over a comparatively long spinningperiod, no dimculties are encountered caused by deposition of solidmaterials at the spinneret face.

In all of the above examples a conventional lead spinning trough, leadheating coils and other usual equipment are employed. The spinnerets areoperated over a period of 24 to 72 hours. Experience with similarspinning conditions but employing a bath containing lead and sulfide inquantities normally contained in such a bath necessitates cleaning andchanging of spinnerets about once every eight hours.

The filtration of the bath is carried out with the use of a carefullyprepared filter and under such conditions as to remove as much suspendedmaterial as possible, including insoluble lead sulfide, lead sulfate,and sulfur. Filtration of the bath is critical in the sense that itshould be carefully done to insure substantially complete removal of theinsoluble materials. Any type of filter may be employed if it iscarefully prepared and contains sufilcient filtering material for thepurpose specified. For example, satisfactory filters may be preparedwith carefully packed excelsior, or wood shavings, sand, activatedcarbon, or the like. In practice, excellent results have been obtainedby the use of a filter made up of selected graded sizes of anthracite.Settling tanks, centrifugal force, or any other means of clarificationmay be employed, where practical, to efiect the same result. Theturbidity of the filtrate should be as low as possible and shouldpreferably not exceed 25 parts per million as determined by the methodsdescribed in Standard Methods of Water Analysis (8th ed., 1936, AmericanPublic Health Association), if the maximum benefits of the invention areto be realized.

Particularly good filtration is obtained, as mentioned above, by the useof an anthracite filter. Such a filter unit may advantageously consistof a closed tank, about 8 feet in diameter, essen- 'tially cylindricalbut having suitably concave ends which serve as the top and bottom ofthe tank. The cylindrical middle portion is about 6 feet, 7 inches inaltitude. Inside the tank and supported on a suitable grid or screen thefilter bed is prepared in a manner similar to a conventional sand orgravel filter. Several layers of anthracite, preferably treated withdilute sulfuric acid to remove iron and thoroughly washed, are arrangedas follows from bottom to top:

6 inch layer nut coal 4 inch layer pea coal 3 inch layer buckwheat coal3 inch layer rice coal 3 inch layer barley coal 30 inch layer crushedanthracite of 20 mesh 30inch freeboard from top of coal to limit of cy-=lindrica-l portion of tank from the bottom through suitable manifolds.Preferably a baffle is inserted near the top of the tank to avoiddisturbance of the filter bed. In operation, the filter is used in amanner similar to a conventional gravel filter and may be cleaned bybackwashing in the usual way. Especially good results are secured if theanthracite selected is that sold under the trade name Anthrafilt,"obtainable from the Anthracite Equipment Corporation, New York, NewYork.

If desired, the invention may be modified by deliberately increasing theconcentration of the offensive anion, i. e., the ion tending to form aninsoluble salt with the metal cations present, prior to the filtrationstep. This procedure is especially useful if the purification of thebath is expected in any way to increase the concentration of offensivecation.

For example, part of the bath may be subjected to an evaporation andcrystallization step to reduce its water and sodium sulfate content andsubsequently returned to the main body of the bath as mentioned above.The use of lead equipment in the evaporation step or the addition ofsulfuric acid containing lead may increase the concentration of theoffensive metal cation, or cation tending to form an insoluble salt withthe offensive anion in the bath.

In such a case, the bath, prior to filtration, can be saturated withhydrogen sulfide under pressure, if desired, causing reduction in theconcentration of the offensive cation and possibly precipitation ofsulfur. It is then filtered carefully, also under pressure, if desired,and then aerated to remove the offensive sulfide anion. The bath willthen be eminently suited for use.

For the removal of offensive sulfide anion, aeration has been proposedabove. This procedure will remove hydrogen sulfide in part by mechanicaldisplacement and in part by oxidation to sulfur. If the amount of sulfurliberated is excessive, the bath may be filtered again for clarificationpurposes. The offensive sulfide anion may be removed by mild oxidationreactions, such as by means of hydrogen peroxide, persulfuric acid,chlorine, electrolysis, etc., so long as the oxidizing agent does notintroduce some other offensive cation into the bath.

The aeration or other oxidation of the bath is conveniently carried outin a suitably large open-top tank. When aeration is used the tank may beprovided with perforated pipes near the bottom through which air may beblown. If air is introduced under a pressure of about 20 pounds persquare inch, 8. flow of air in the ratio of about 1 cubic foot perminute for every 57 gallons per minute of bath fiow will yieldsatisfactory results. If air under pressure of only 3-5 pounds persquare inch is used, a ratio of about 1 cubic foot per minute of air forevery 1.5-2.0 gallons per minute of bath flow will yield effectiveaeration. Such aeration is easily capable of lowering the reducing powerof the bath (as hereinafter defined) from as much as 100 parts permillion of sulfide ion to less than parts per million.

The removal of offensive ions in the bath can be accomplished in otherways than those spe cifically described above. For example, cations, aswell as anions, may be removed by electrolysis of the bath in a knownmanner, or by other means of precipitation and filtration. The offensiveanion may be removed, as stated above,

.by an oxidation reaction other than aeration. In

other offensive ions are not thereby introduced into the bath.

Since the formation of these insoluble salts, such as lead sulfide, isdependent on the concentrations of the cations and anions in solution inthe regenerating bath according to the chemical principle of massaction, their formation can be minimized, if not prevented, bymaintaining the concentration of either the offensive,insolublesalt-forming cations or anions or both so low that theirsolubility product is not exceeded in the vicinity of the spinneretface.

Similarly, it will be understood that if the concentration of anoffensive cation, for example, is sufficiently low, the tolerableconcentration of the offensive anion may be considerably higher thanwould be the case if the offensive cation concentration were high. Thereverse situation is also true. Consequently, if both concentrations aremaintained at as low a figure as possible, the chances of not exceedingthe solubility product in the reaction zone at the face of the spinneretwill be enhanced.

While it is preferable to keep both the lead and sulfide concentrationsas low as possible, beneficial results are obtained when one is high,provided the other is low. Thus, if the total load concentration is only2 parts per million, a reducing power, calculated as a function ofsulfide ion concentration, as high as 30 parts per million may betolerated while, if the lead content is 8 parts per million, thereducing power should not exceed 10 parts per million. A total leadcontent as high as 8 parts per million may be tolerated if the sulfideconcentration does not exceed about '7 parts per million measured asherein described. It has been found, as a general rule, that the productof the lead concentration in parts per million and the sulfideconcentration in parts per million should be maintained less than 60.

The regenerating bath is, of course, preferably fed to the spinningmachine at such a rate that the accumulated offensive sulfide ionconcentration is less than that of a bath saturated with hydrogensulfide until the bath has passed the last spinneret, or spinningposition, and is ready for purification and recirculation. However, ifno appreciable lead ion is picked up by the bath, little harm willobtain even if the bath becomes saturated with the offensive anionbefore the last spinning position is reached, for there will beinsuflicient offensive cation present to form appreciable amounts ofinsoluble salt in the reaction zone at the spinneret face and thebenefits of the invention will still be enjoyed to a major extent. Ifthe offensive metal cation content, particularly the lead content, ofthe bath is maintained at less than 4 parts per million without theintroduction of other offensive metal ions very material diminution ofdeposition of insoluble foreign matter on the spinneret face will beaccomplished. If each spinneret is provided continuously with freshbath, as by means of the so-called crossfiow bath, i. e., a bath inwhich the bath is passed into the regenerating bath tank on the side ofsaid tank where the spinnerets are positioned and removed on theopposite side of the tank, the pick-up of offensive ions can beminimized.

It will be readily apparent that it is not essen tial to remove theoffensive ions from all of the coagulating bath. It will be sufficientif that part of the bath which is in contact with the spinneret istreated for removal of such offensive ions. The portion of the bathadjacent the spinnerets may. for example, be partitioned off from theremainder of the bath and the offensive ions removed only from thatportion of the bath which is in contact with the spinnerets.Alternatively, the two-bath system for coagulation of the filaments maybe employed in which the ofiensive ions are removed only from the firstbath.

The invention has been described in terms oi the viscose process for themanufacture of rayon filaments involving the use of a regenerating bathin which the principal offensive cations and anions are lead and sulfideions respectively. However, the invention is also applicable when otherofiensive ions are involved, such as cadmium, bismuth, copper, thallium,or even silver or mercury. Furthermore, if zinc ions, or other metalions, are undesirable but necessarily present in the process, theconcentration of the zinc, or other metal, can be controlled to obtain areduction in cratering, caused by deposition of insoluble salts of thesemetals, in accordance with the present invention. Similarly, a differentwet spinning process involving other offensive anions, such as sulfite,sulfate, carbonate, or the like will find the principles of thisinvention applicable.

Since it i obvious that many changes and modifications can be made inthe above-described details without departing from the nature and spiritof the invention, it is to he undertsood that the invention is not to belimited to the details described herein except as set forth in theappended claims.

I claim:

1. The process of spinning regenerated cellulose filaments whichcomprises extruding viscose through a spinneret into an acid bathcomprising a bath liquid containing lead ions and hydrogen sulfide,removing said bath liquid from said bath, saturating the bath liquidwith hydrogen sulfide under pressure, filtering the bath liquid underpressure through an anthracite filter for the removal of lead sulfidefrom said bath liquid, and then removing hydrogen sulfide by aeration.

2. The process of spinning regenerated cellulose filaments whichcomprises extruding viscose through a spinneret into an acid bathcomprising a bath liquid which contains heavy metal cations and anionswhich are capable of combining to form therein an insoluble metal saltand which bath liquid is subject to accumulationof said ions in anamount to exceed the solubility product of said ions to form saidinsoluble metal salt in the reaction zone at the face of the spinneret,removing said bath liquid from said bath, increasing the said anioncontent of the bath liquid to form said insoluble metal salt, filteringsaid insoluble metal ,salt from said bath liquid, then removing saidanions from said bath liquid, and then returning said bath liquid backinto said bath.

3. The process of spinning regenerated cellulose filaments whichcomprises extruding viscose through a spinneret into an acid bathcomprising a bath liquid which contains lead ions and anions which arecapable of combining to form therein an insoluble lead salt and whichbath liquidis subject to the accumulation of said ions in an amount toexceed the solubilityv product of said ions to form said insoluble leadsalt in the reaction zone at the face of the spinneret,

then returning said bath liquid back into said bath.

4. The process of spinning regenerated cellulose filaments whichcomprises extruding viscose through a spinneret into an acid bathcomprising a bath liquid which contains heavy metal cations and sulfideions which are capable of combining to form therein an insoluble metalsulfide and which bath liquid is subject to the accumulation of saidions in an amount to exceed the solubility product of said ions to formsaid insoluble metal sulfide in the reaction zone at the face of thespinneret, removing said bath liquid from said bath, increasing thesulfide ion content of the bath liquid to form said insoluble metalsulfide, filtering said insoluble metal sulfide from said bath liquid,then removremoving said bath liquid from said bath, in-

ing sulfide ions from said bath liquid, and then returning said bathliquid back into said bath 5. The process of spinning regeneratedcellulose filaments which comprises extruding viscose through aspinneret into an acid bath comprising a bath liquid which contains leadions and sulfide ions and which bath is subject to the accumulation ofsaid ions in amounts exceeding the solubility product of said ions toform insoluble lead sulfide in the reaction zone at the face of thespinneret, removing said bath liquid from said bath, increasing thesulfide ion content of the bath liquid to form said insoluble leadsulfide, filtering said insoluble lead sulfide from said bath liquid,then removing sulfide ions from said bath liquid, and then returningsaid bath liquid back into said bath.

6. The process of spinning regenerated cellulose filaments whichcomprises extruding viscose through a spinneret into an acid bathcomprising a bath liquid which contains lead ions and sulfide ions andwhich bath liquid is subject to the accumulation of said ions in amountsexceeding the solubility product of said ions to form insoluble leadsulfide in the reaction zone at the face of the spinneret, removing saidbath liquid from said bath, passing hydrogen sulfide into said bathliquid to increase the sulfide ion content of said bath liquid and forminsoluble lead sulfide, filtering said insoluble lead sulfide from saidbath liquid, then removing hydrogen sulfide from said bath liquid, andthen returning said bath liquid back into said bath.

7. The method of diminishing the deposition of insoluble metal salt on aspinneret in the spinning of regenerated cellulose filaments fromviscose which is extruded into an acid spinning bath comprising a bathliquid containing anions and heavy metal cations capable of combining toform therein an insoluble metal salt and which bath is subject to theaccumulation of said ions in an amount to exceed the solubility productof said ions to form said insoluble metal salt in the reaction zone atthe face of the spinneret, the steps comprising removing the bath liquidfrom said bath, filtering said bath liquid in the presence of saidaccumulated anions to remove accumulated insoluble metal salt therefrom,then removing said accumulated anions from said bath liquid, andreturning said bath liquid to said bath.

8. The method oi? diminishing the deposition of insoluble metal salton aspinneret in the spinning of regenerated cellulose filaments fromviscose which is extruded into an acid spinning bath comprising a bathliquid containing anions and lead ions capable of combining to formtherein an insoluble lead salt and which bath is sub- .lect to theaccumulation of said ions in an amount to exceed the solubility productof said ions to form said insoluble lead salt in the reaction zone atthe face of the spinneret. the steps comprising removing the bath liquidfrom said bath, filtering said bath liquid in the presence ofaccumulated anions to remove said accumulated insoluble lead salttherefrom, then removing said accumulated anions from said bath liquidand returning said bath liquid to said bath.

9. The method of diminishing the deposition of insoluble metal salt on aspinneret in the spinning of regenerated cellulose filaments fromviscose which is extruded into an acid spinning bath comprising a bathliquid containing sulfide ions and heavy metal cations capable ofcombining to form therein an insoluble metal sulfide and which bath issubject to the accumulation of said ions in an amount to exceed thesolubility product of said ions to form said insoluble metal sulfide inthe reaction zone at the face of the spinneret, the steps comprisingremoving the bath liquid from said bath, filtering said bath liquid inthe presence of accumulated sulfide ions to remove accumulated insolublemetal sulfide therefrom, then removing accumulated sulfide ions fromsaid bath liquid, and returning said bath liquid to said bath.

10. The method of diminishing the deposition of insoluble metal salt ona spirmeret in the spinning of regenerated cellulose filaments fromviscose which is extruded into an acid spinning bath comprising a bathliquid containing sulfide ions and lead ions capable of combining toform therein insoluble lead sulfide and which bath is subject to theaccumulation of said ions in an amount to exceed the solubility productof said ions to form said insoluble lead sulfide in the reaction zone atthe face of the spinneret, the steps comprising removing the bath liquidfrom said bath, filtering said bath liquid in the presence ofaccumulated sulfide ions to remove accumulated lead sulfide therefrom,then removing accumulated sulfide ions from said bath liquid andreturning said bath liquid to said bath.

11. The method of diminishing the deposition of insoluble metal salt ona spinneret in the spinning of regenerated cellulose filaments fromviscose which is extruded into an acid spinning bath comprising a bathliquid containing hydrogen sulfide and heavy metal cations capable ofcombining to form therein insoluble lead sulfide and which bath issubject to the accumulation of said hydrogen sulfide and lead ions in anamount to exceed the solubility product of the sulfide ions and leadions to form said insoluble lead sulfide in the reaction zone at theface of the spinneret, the steps comprising removing the bath liquidfrom said bath, filtering said bath liquid in the presence ofaccumulated hydrogen sulfide to remove accumulated insoluble leadsulfide therefrom, then removing accumulated hydrogen sulfide from saidbath liquid, and returning said bath liquid to said bath.

12. The method as defined in claim 7 in which the said anions areremoved by aeration of the bath liquid.

13. The method as defined in claim 8 in which the said anions areremoved by aeration of the bath liquid.

14. The method as defined in claim 9 in which the sulfide ions areremoved by aeration of the bath liquid.

15. The method as defined in claim 10 in which the sulfide ions areremoved by aeration of the bath liquid.

16. The method as defined in claim 11 in which the hydrogen sulfide isremoved by aeration of the bath liquid.

ISAAC F. WALKER.

